1. Field of the Invention
The present invention belongs to the technical field of power electronics, in particular relates to a double auxiliary resonant commutated pole three-phase soft-switching inverter circuit and a modulation method.
2. The Prior Arts
The power electronic technology is a technology that achieves effective utilization of electric semiconductor devices by applying circuit principles and design theory and analyzing development tools so as to efficiently transform and control electric energy. Because the modern power electronic device increasingly tends to miniaturization and light weight, high frequency of the inverter has become its important development trend. The increase of the operating frequency helps to improve performance and reduce volume for the inverter. But with the continuous increase of the switching frequency, switching loss will also be increased in proportion. In addition, noise pollution and electromagnetic interference (EMI) problems also become increasingly obvious. Aiming at the above problems, the soft-switching technology is introduced into the inverter. With the continuous development of the soft-switching inversion technology, all kinds of soft-switching inverter topological structures successively appear. In numerous soft-switching inversion topologies, an auxiliary resonant commutated pole inverter does not increase the original voltage and current stress of a main power switching device, is more suitable for high-power inversion occasions and is therefore generally concerned by researchers of relevant fields in countries of the world.
An active auxiliary resonant commutated pole inverter proposed earlier needs to use two large electrolytic capacitors, brings the problem of neutral-point potential change for the inverter and needs individual detection circuit and logic control circuit. An improved auxiliary resonant commutated pole inverter that appears subsequently, such as transformer auxiliary inverter, coupled inductor inverter, triangular or star-shaped resonance absorbing inverter, etc., either a complicated coupled inductor or transformer and a corresponding magnetic flux reset circuit are needed or mutual coupling is needed among three phases of resonant circuits, resulting in that the main circuit and the control strategy become complicated. So far, in numerous three-phase auxiliary resonant commutated pole soft-switching inverter topological loops, two main switching tubes of the same bridge arm share one set of auxiliary resonant elements and the quantity of the auxiliary elements is less, so the inverter is suitable for medium and small power occasions.
A novel auxiliary resonant pole inverter topological structure is disclosed in Chinese Journal of Scientific Instrument, Volume 30, No. 6, 2009, Chinese Journal of Electrical Engineering, Volume 33, No. 12, 2013 and IEEE Transactions on Power Electronics, Volume 29, No. 3, 2014. The circuit diagram of the inverter is shown in FIG. 1. A set of auxiliary resonant commutator circuit is arranged in each phase of three phases of circuits in the auxiliary resonant pole inverter. Each phase of auxiliary resonant commutator circuit consists of two main resonant capacitors, two auxiliary resonant capacitors, two auxiliary resonant inductors, two auxiliary switching tubes and four auxiliary diodes. The inverter avoids two large electrolytic capacitors used in a traditional resonant pole inverter and has the advantages that three phases of auxiliary resonant commutator circuits are independently controllable, load current is not required to be detected, soft switching of the switching tubes can be achieved within the range of full load, the voltage stress of each element is not greater than DC input voltage, etc. In addition, each of two main switching tubes of the same bridge arm of the inverter has a set of auxiliary resonant elements so that the power level of the inverter can be further enhanced. Therefore, the inverter is more suitable for high-power occasions. However, the auxiliary resonant pole inverter still has disadvantages: the ZVS turn-off of the auxiliary switching tubes is achieved on the premise that the parasitic inductance and the parasitic capacitance of the auxiliary resonant commutator circuits are zero, but in practical application, because of the influence of the parasitic inductance and the parasitic capacitance introduced by wiring form, the ZVS turn-off condition of the auxiliary switching tubes will be damaged and reliable ZVS turn-off cannot be achieved. Particularly, the longer the distance between the auxiliary switching tubes and the auxiliary resonant capacitors and the distance between the auxiliary switching tubes and the DC power supply are, the greater the influence of the parasitic inductance brought by loop wiring is. This influence is especially apparent along with high capacity of the device, and is also a key problem that has to be solved in future practical application.
Aiming at the above problems, Research on An Active Double Auxiliary Resonant Commutated Pole Soft-switching Inverter is disclosed in 2014 by IEEE 23rd International Symposium on Industrial Electronics (ISIE). The topological structure of the inverter is shown in FIG. 2 (for the convenience of narration, the topological structure is hereinafter called the original topology). The auxiliary resonant commutator circuit of the auxiliary resonant commutated pole inverter consists of two main resonant capacitors, two first auxiliary resonant capacitors, two second auxiliary resonant capacitors, two first auxiliary resonant inductors, two second auxiliary resonant inductors, two auxiliary switching tubes and eight auxiliary diodes. The topological loop of the inverter can effectively avoid the influence caused by the parasitic inductance and the parasitic capacitance of the loop brought by the wiring form of the loop on ZVS turn-off of the auxiliary switching tubes, thereby ensuring that the auxiliary switching tubes reliably achieve ZVS turn-off.
However, the original topology still has disadvantages: in order to achieve the soft switching of the switching tubes, the auxiliary resonant commutator circuits shall flow through resonant current, so the current that actually flows through the auxiliary resonant commutator circuits is the sum of the resonant current and the load current at the moment of current commutation. Therefore, within the range of full load, even in no load condition, the auxiliary resonant commutator circuits shall flow through high resonant current. The resulting conduction loss has become an important reason for limiting the increase in efficiency of the auxiliary pole inverter, and is also a key problem that has to be solved in future practical application.